The present invention relates generally to chemical mechanical polishing of substrates, and more particularly to a carrier head for use in chemical mechanical polishing.
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, it is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly nonplanar. This nonplanar surface presents problems in the photolithographic steps of the integrated circuit fabrication process. Therefore, there is a need to periodically planarize the substrate surface.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head, and pressed against a rotating polishing pad. The polishing pad may comprise an abrasive surface. An abrasive chemical solution or slurry may be introduced onto the polishing pad to assist the polishing process. The slurry should be distributed in a substantially uniform layer across the polishing pad. This improves the uniformity of planarization.
In one aspect, the invention is directed to a carrier head for a chemical mechanical polishing apparatus. The carrier head has a substrate receiving surface, a retaining ring surrounding the substrate receiving surface, and a slurry reservoir formed on the carrier head. The reservoir is in fluid communication with a bottom surface of the retaining ring to direct a polishing slurry from the reservoir to a polishing pad.
Implementations of the invention may include the following features. The reservoir may be formed in an upper surface of a housing the carrier head, in a top surface of a slurry supply member that surrounds the retaining ring, or in a top surface of the retaining ring. A passage may be formed through the housing, the retaining ring and/or the slurry supply member. The slurry may be directed from the reservoir to a bottom surface of the retaining ring or to a bottom surface of the slurry supply member. A channel may be formed in the bottom surface of the retaining ring or the slurry supply member to direct slurry inwardly.
In another aspect, the invention is directed to a retaining ring for a carrier head. The retaining ring has an annular body having an inner surface to retain a substrate, a trough in an upper surface of the retaining ring, and a plurality of channels extending through the retaining ring from the trough to a lower surface of the retaining ring.
Implementations of the invention may include the following features. Each channel can terminates in a groove in the lower surface of the retaining ring. A lip in the trough can retain the slurry in the trough as the retaining ring rotates.
In another aspect, the invention is directed to a carrier head for chemical mechanical polishing that has a substrate receiving surface, a retaining ring surrounding the substrate receiving surface, and at least one channel through the retaining ring to fluidly couple a trough in the carrier head to a bottom surface of the retaining ring to dispense a polishing slurry on a polishing pad.
Implementations of the invention may include the following features. There may be a plurality of channels. The trough may include a lip to contain the polishing slurry as the carrier head is rotated. The polishing slurry may be metered into the trough at a rate in the range of about 25-100 ml/min, or gravity fed into the trough at a rate in the range of about 25-100 ml/min. A tube may connect a passage in a carrier head drive shaft to the trough. An inwardly extending groove may be formed in the bottom surface of the retaining ring carry and fluidly coupled to the at least one passage. A circular groove may be formed in the bottom surface of the retaining ring carry and fluidly coupled to the at least one passage.
In another aspect, the invention is directed to a chemical mechanical polishing apparatus. The apparatus has a polishing pad and a carrier head. The carrier head includes a substrate receiving surface, a retaining ring surrounding the substrate receiving surface, a trough on a top surface of the retaining ring, and at least one channel to fluidly couple the trough to a bottom surface of the retaining ring to dispense a polishing slurry on a polishing pad. An arm extends over the polishing pad to dispense a polishing slurry into the trough.
Implementations of the invention may include the following features. The arm may be pivotally connected to a machine base.
In another aspect, the invention may be directed to a method for a chemical mechanical polishing apparatus. In the method, a polishing slurry is directed through a passage in a retaining ring onto a polishing pad.
Implementations of the invention may include the following features. Polishing slurry may be dispensed into a trough on the retaining ring which is in fluid communication with the passage. The polishing slurry may be dispensed continuously, e.g., at a rate in the range of about 25-100 ml/min, or intermittently, e.g. with a sufficient slurry to polish a preselected number of substrates.
The present invention advantageously provides slurry to an area near the interface between a substrate and a polishing pad. The slurry-containing trough evenly and uniformly distributes the slurry on the polishing pad. Due to such distribution of the slurry, the CMP apparatus will planarize substrates more uniformly, imparting the attendant benefits of improved planarization. The invention also advantageously conserves the amount of polishing slurry used. Polishing slurry is an expensive consumable, and it is conserved by applying it to the substrate/polishing pad interface, rather than over the entire pad surface. By reducing the amount of slurry applied to the pad, the CMP apparatus is more likely to remain relatively clean and free of dried slurry, thereby reducing the likelihood of damage to the substrate.
Additional advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention may be realized by means of the instrumentalities and combinations particularly pointed out in the claims.